In recent years a number of vascular prostheses have been developed that may be deployed in a patients' vessel or organ following a mechanical dilatation procedure.
For example, percutaneous transluminal angioplasty (PTA) is commonly used today as an alternative treatment to traditional coronary artery bypass grafting. Typically, such procedures involve the insertion of a balloon catheter within a constricted vessel, such as a coronary artery, and dilation of the balloon to disrupt plaque lining the vessel, thereby increasing the diameter of the vessel and restoring flow therethrough. It is common practice to then deploy a vascular prosthesis, such as the Palmaz-Schatz Stent.RTM. sold by Johnson & Johnson Interventional Systems, Inc., to maintain the expanded diameter of the vessel. That stent comprises a slotted metallic tubular member that is plastically deformed using a balloon catheter to maintain the patency of the vessel.
Circumstances frequently arise, when using the above prosthesis, in which the prosthesis is not completely expanded within the vessel prior to withdrawal of the delivery catheter. It also frequently occurs that a prosthesis, once implanted within a body lumen, experiences some constriction. In these instances, it is frequently desirable to re-expand the prosthesis using a subsequently inserted balloon catheter or other means for expanding the prosthesis.
Difficulties arise, however, when trying to position a dilatation device (i.e., balloon catheter) within a previously deployed prosthesis to fully expand or re-expand the prosthesis. In particular, if the dilatation device is not properly centered within the prosthesis, the prosthesis may not be evenly expanded, thus causing the prosthesis to assume the form of a frustrum of a cone, rather than a cylinder. In extreme situations, the narrower end of this frustrum may even become tilted away from the wall of the body lumen, creating sites for enhanced thrombolytic action.
A further difficulty arises when the prosthesis was previously deployed in a tortuous vessel, since it may be difficult to determine when the dilatation device is properly centered in the prosthesis using only the two-dimensional view provided by conventional fluoroscopy and dye techniques.
In addition, it would be desirable to provide apparatus and methods for determining the location of a previously deployed prosthesis to effect further treatment. For example, U.S. Pat. No. 5,122,136 to Guglielmi et al., incorporated herein by reference, describes detachable coils for use in treating aneurysms (hereinafter "GDC aneurysm coil"). It would be desirable to provide apparatus for determining the location of a previously deployed GDC aneurysm coil, for example, to add further material within the aneurysm.
It would also be desirable to determine the location of a previously deployed prosthesis to enable repositioning of a therapeutic device. For example, it has been suggested to provide localized radiation treatment using radioactive stents. It accordingly may be advantageous to locate such stents that have been previously deployed, for example, to retrieve the stent at the end of a desired period of exposure.
In view of the foregoing, it would be desirable to provide methods and apparatus for positioning a therapeutic device within a body lumen to enable a clinician to accurately determine when the therapeutic device is properly aligned with a previously deployed prosthesis.
It further would be desirable to provide methods and apparatus for enabling a clinician to accurately deploy a dilatation device within a previously deployed prosthesis to enable uniform re-expansion of the prosthesis along its length.
In addition, it would be desirable to provide methods and apparatus for accurately determining placement of a therapeutic device within a previously deployed prosthesis, such apparatus constituting an inexpensive modification of previously known catheter systems.